1. The Field of the Invention.
The field of the invention relates to the dehologenating of halogenated hydrocarbons by their treatment with liquid sodium. Accordingly the general objectives of the present invention are to provide a novel and improved method of such character.
2. Description of the Prior Art.
The background art of the invention reveals the well-known Wurtz-Fitting reaction, and its precursor the Wurtz reaction, in which soduim is reacted with an alkyl or aryl halide and more recently, commercially, various attempts at elimination and destruction of polychlorinated bi-phenyls (PCB's), highly toxic environmental polutants, from oil, and particularly transformer oil. Reference is made to U.S. Pat. Nos. 4,337,368 to Pytlewski et al, 4,340,471 to Jordan, 4,377,471 to Brown and 4,379,752 to Norman. These methods are generally characterized by reactions which attempt to strip away chlorine from the aromatic ring structure of PCB's leaving, inter alia, a non-chlorinated byphenyl, benzene, chloro-benzene, some of which may be themselves environmentally harmful, and sodium chloride.
The Wurtz-Fitting reaction is well-known and may be summarized generally by:
1. EQU RX+Na.fwdarw.RNaX+H.sup.+
2. EQU RNaX+H.sup.+ .fwdarw.RH+NaX
or alternatively:
2a. EQU 2RNax.fwdarw. R--R+2NaX.
The reaction is conducted at temperatures above 97.7.degree. C., the melting point of sodium. A stoichiometric amount of sodium is added to the organic halide based upon an estimate of the amount of halogen to be removed. An excess of sodium is desirable and may be readily removed by subsequent cooling, filtration and destruction by, for example, sulfuric acid.
In the laboratory, the Wurtz-Fitting reaction is characterized by poor yields and other disappointing results.
One of the basic problems encountered, which the present invention solves, has been the uncontrolled formation of undesirable free radicals occasioned by the inadvertent presence of various contaminants, as well as sodium, and a consequent undesirble polymerization or combination of such radicals.
An objective of the present invention is to increase the yield of de-halogenated hydrocarbons. A further object is to reduce large polymer by-products possible in the reaction simultaneously therewith by controlled hydrogenation of free radicals which are the natural remnants of the destructive reaction process. Previous efficiencies of reaction have been reported up to 75%, based upon starting temperature, time, and purity of the hydrocarbonaceous component.
Yields in excess of 99% have been observed by the present invention. Factors previously taken into account by those skilled in the art have been particle size of the sodium prior to its liquifaction, control of the contact of pure sodium with air prior to its addition into the reaction vessel, the effect of moisture upon sodium generally and the recommended use of nitrogen as a blanket over the surface of the reactants. Particular importance has been attached to the maintenance of pre-liquidus sodium at particle sizes below 10 microns in diameter. Attention is directed to U.S. Pat. No. 4,379,752 to Norman in which reference is made to the text of Fatt and Tashima, "Alkali Metal Dispersions," Van Nostrand (New York, 1961). The hazard of sodium in the presence of moisture wherein the dangerous evolution of hydrogen gas and the formation of sodium hydroxide is well-known. However, those ordinarily skilled in the art invariably fail to de-water the halide as a preliminary step but sometimes do so post-reaction. Such a failure, however, causes the unwanted consumption of sodium. The presence of the hydroxide also appears to inhibit the dehalogenation.
The use of nitrogen, in lieu of air, over the surface of the reaction medium, has been thought to eliminate problems caused by moisture in the air as well as oxygen in contact with the sodium wherein sodium oxide is rapidly and undesirably formed. Your inventor has found that nitrogen will in fact substantially affect the reactive process and it must be avoided if yields above 75% are to be had. Use of dry argon or helium in place of the nitrogen as the current invention teaches has a significant effect on yield allowing achievement in excess of 99%
The method disclosed in this application provides an efficient and rapid means for the destructive dehalogenation of hydrocarbons.